Integrated circuits are typically formed on a semiconductor substrate such as a silicon wafer or other semiconducting material. A continuing goal in integrated circuit processing is to reduce the size of individual electronic components thereby enabling smaller and denser integrated circuitry. One technique for patterning and processing semiconductor substrates is photolithography. Photolithography processes include deposition of a patternable mask, such as a photoresist mask that is used to form patterns on semiconductor substrates. Photoresist materials can be processed to modify their solubility in certain solvents. For example, portions of a photoresist mask can be exposed to radiation to change the solvent solubility of the exposed regions versus the unexposed regions. Thereafter, the exposed or unexposed regions can be removed, depending on the type of photoresist, leaving masking patterns of the photoresist on the semiconductor substrates. Such processes can be repeated and/or coupled with other semiconductor processing steps to form features in semiconductor substrates.
The continual reduction in feature sizes of integrated circuits places ever greater demands on the techniques used to form the features. For example, photolithography is commonly used to form patterned features, such as conductive lines. A concept commonly referred to as “pitch” can be used to describe the sizes of the repeating patterned features in conjunction with adjacent spaces. Pitch may be defined as the distance between an identical point in two neighboring features of a repeating pattern, thereby including the maximum width of the feature and the adjacent space. However, due to factors such as optics and light or radiation wavelength, photolithography techniques tend to have a minimum pitch below which a particular photolithographic technique cannot reliably form features. Thus, minimum pitch of a photolithographic technique is an obstacle to continued feature size reduction using photolithography.
Directed self-assembly (DSA) materials are being studied for use in extending the capabilities of photolithographic techniques beyond their minimum pitch. Specifically, DSA materials may be formed over photographically defined guide patterns to reduce pitch between structures to less than that of the minimum photolithographic feature size. Particular DSA materials of note include copolymers containing two (or more) chemical components that have controlled sizes. These components can be bonded together into polymer chains known as diblocks, such as A-A-A-A-A-A-A-B-B-B-B-B-B-B, where A and B represent monomers. When formed over a guide pattern, the A and B monomers of a diblock copolymer are relatively disordered. However, these monomers (A and B) can be induced to separate into distinct phases and thereby form features with a characteristic dimension that is defined by the chemical composition of the guide pattern. By coating a diblock copolymer, or other DSA material, over a guide pattern, it is possible to “interpolate” the features between the guide patterns and reduce the pitch by a factor of 2-10 relative to the guide pattern. This can significantly reduce the cost and complexity of the processing that is used to create high resolution patterns.
However, known methods for creating DSA guide patterns have some limitations. For instance, existing processes for creating guide patterns typically involve plasma processing, low-throughput steps, or other processing that can increase the cost and complexity of the manufacturing process.
Accordingly, it is desirable to provide improved methods for fabricating guide patterns for fabricating integrated circuits. Further, it is desirable to provide methods for fabricating guide patterns for use with DSA materials to form masks having features smaller than the minimum feature size of current photolithographic processes. Also, it is desirable to provide methods for fabricating integrated circuits using masks formed with features smaller than the minimum photolithographic feature size. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.